1. Field of the Invention
The present invention relates to a cooling system for a water-cooled type of internal combustion engine, and in particular, to a sealed cooling water recirculation system using a reservoir tank.
2. Description of the Related Art
In a known cooling system for an internal combustion engine, a cooling water reservoir tank is provided and is used not only for storing an overflow of cooling water but also for ensuring a recirculation of a part of the cooling water to the reservoir tank, to thereby separate and remove air and vapor from the cooling water in the reservoir tank, whereby the cooling efficiency of the cooling system is increased. (See Japanese Unexamined Utility Model Publication No. 52-90654, Japanese Unexamined Utility Model Publication No. 60-15922, Japanese Unexamined Utility Model Publication No. 62-88829, Japanese Unexamined Utility Model Publication No. 56-99009, and Japanese Unexamined Utility Model Publication No. 59-81985.)
In this type of cooling system, in general, an independent cooling water passageway connects the reservoir tank to an engine body and a radiator, and the reservoir tank is provided with a cap equipped with a relief valve which allows air or vapor held in an upper portion of the reservoir tank to be discharged to the atmosphere, when the pressure inside the reservoir tank exceeds a predetermined value, and thus prevents an excessive increase of the pressure in the cooling system. This operation also allows air to be quickly separated from the cooling water: this air is entrained in the cooling system when the cooling water is supplemented, and remains in the cooling system. The separated air is discharged by the relief valve in the reservoir tank, and thus the cooling efficiency of the system is enhanced.
When the engine is stopped just after a high load operation, the circulation of the cooling water is stopped, and accordingly, the temperature of the cooling water becomes very high, which causes a large amount of the cooling water to be vaporized, and this vapor collects in the upper portion of the cooling system (i.e., a hot soak). In the prior art construction, it is difficult to quickly remove the vapor, since the pipe connecting the upper portion of the cooling water jacket of the engine to the reservoir tank runs vertically downward from the reservoir tank and then upward to a union with the water jacket of the engine, and as a result, a vapor lock often occurs in a portion of the pipe just after the hot engine is stopped. This vapor lock in the engine cooling water system causes a reverse flow of the cooling water in the engine toward the reservoir tank, and the excess cooling water in the tank overflows to the outside via the relief valve.
This loss of the cooling water will, of course, lower the cooling efficiency and reduce the reliability of the device, since essentially the object of the sealed type cooling system provided with the reservoir tank is to eliminate the need to supplement the water in the system.